>>528132614
Look at the bangboo's second skill, which always defines it. Most often, the skill activates when you have one or two characters from the same faction. For instance, Belion needs two Yunkui characters on the team to get a fat damage boost (or one, if you get more than two dupes). In the end, you will rarely ever swap bangboos (one will always be stuck to its designated team), so it makes sense to try and max out the one you actually use before rolling others.